In the hydrometallurgical treatment of ores containing nickel cobalt and/or copper, by-product sulfides containing the metals cobalt, nickel and/or copper may be generated in various points in the process. As an example, the purification of nickel bearing ammoniacal leach liquors to remove cobalt and copper can produce precipitates which are usually in the form of a thickener underflow or a filter cake and which contain up to 75% moisture. These materials are finely divided and may include, besides the valuable metals cobalt, nickel and copper various other impurities and residual ammonia. These materials are difficult to treat and at present the only known ways of treating them for the purpose of recovering metal values involve leaching at elevated temperature and pressure. Such a process is described in a paper presented at 109 AIME Annual Meeting, Las Vegas, Nev., U.S.A. in February, 1980 by Suetsuna et al. Treatment of materials at elevated temperature and pressure in autoclaves is expensive and it would be desirable to provide a means for treating nickel, cobalt, copper sulfide residues at atmospheric pressure. In this connection the atmospheric leaching of mattes is known and is described for example in a paper entitled, "Atmospheric Leaching of Matte at the Port Nickel Refinery" by Llanos et al., which appeared in the CIM Bulletin, February, 1974, pages 74-81. The known atmospheric leaching processes seem to involve the treatment of matte with an acid solution having a high copper content such as spent copper electrowinning electrolyte depleted with respect to copper and having a considerable content of acid. When such such solutions are reacted with matte, a cementation reaction occurs with precipitation of the copper content of the solution and solubilization of nickel and cobalt values in the matte. The economic utilization of such a process depends, of course, on the ready availability of acid solutions containing copper. It is also known from the work of Dr. -Ing Hans Grothe dating back to the 1930's (German Pat. No. 595,688) that ammonia may be used in the treatment of a water solution of cobalt and nickel sulfates to precipitate cobalt and provide a cobalt precipitate depleted in nickel and a solution enriched in nickel and depleted in cobalt. U.S. Pat. No. 3,751,558 is also relevant.
Materials to the treatment of which the invention is particularly directed will usually contain, on a dry basis, about 0.5% to about 15% cobalt, about 5% to about 30% nickel up to about 25% copper, up to about 15% iron and about 15% to about 30% sulfur. The materials usually occur as a result of sulfide precipitation from solution to recover the metal content thereof. The materials may also contain up to about 8% ammonia from prior processing.